Calibration apparatus and calibration method

Abstract

A calibration apparatus includes an insertion portion into which a measurement probe is inserted and a reference reflection plate that is arranged at a position away from a distal end of the measurement probe by a predetermined distance in a state in which the measurement probe has been inserted in the insertion portion and that has uniform reflectivity of light in a range of a wavelength to be measured in an irradiation plane of an illumination light, wherein a material forming the reference reflection plate has a scattering mean free path that is greater than a spatial coherence length at the predetermined distance.

What is claimed is:  
     
       1. A calibration apparatus configured to obtain a plurality of calibration data during correction of returned light from an object to be measured by an optical measurement apparatus, the optical measurement apparatus including: (i) a measurement probe having an illumination fiber that irradiates illumination light at a wavelength to be measured to the object, and a plurality of detection fibers that are arranged to receive, at different angles, the returned light corresponding to the illumination light reflected and/or scattered by the object to be measured; and (ii) a plurality of detectors configured to detect the returned light respectively received by the plurality of detection fibers, the calibration apparatus comprising:
 an insertion portion into which the measurement probe is inserted; and 
 a reference reflection plate that is arranged at a position away from a distal end of the measurement probe by a predetermined distance in a state in which the measurement probe has been inserted in the insertion portion and that has uniform reflectivity of light in a range of the wavelength to be measured in an irradiation plane of the illumination light, wherein: 
 the plurality of detection fibers include a detection fiber arranged adjacent to the illumination fiber, 
 ends of the illumination fiber and the detection fiber are arranged at a position away from the reference reflection plate by a predetermined distance when the measurement probe is inserted in the insertion portion, and 
 a material forming the reference reflection plate has a scattering mean free path that is greater than a spatial coherence length at the predetermined distance. 
 
     
     
       2. The calibration apparatus according to  claim 1 , wherein the material forming the reference reflection plate has the scattering mean free path that is greater than twice the spatial coherence length and has an anisotropic parameter that is equal to or less than 0.85. 
     
     
       3. The calibration apparatus according to  claim 1 , wherein the material forming the reference reflection plate has the scattering mean free path that is approximately equal to twice the spatial coherence length and has an anisotropic parameter is greater than 0.85. 
     
     
       4. The calibration apparatus according to  claim 1 , further comprising:
 a drive unit that moves the reference reflection plate towards the distal end of the measurement probe when the optical measurement apparatus obtains the calibration data. 
 
     
     
       5. The calibration apparatus according to  claim 1 , further comprising:
 an accommodation portion that accommodates the reference reflection plate, wherein the insertion portion and the accommodation portion are connected to each other or arranged changeably between each other. 
 
     
     
       6. The calibration apparatus according to  claim 5 , wherein
 the insertion portion has a light absorption portion provided with, on an inner surface thereof, a light absorption member that absorbs light, the light absorption portion being tubular, and 
 the plurality of calibration data are:
 reference reflection plate calibration data when measurement is performed in the accommodation portion; and 
 internal reflection calibration data of the measurement probe when measurement is performed in the insertion portion. 
 
 
     
     
       7. The calibration apparatus according to  claim 1 , wherein the insertion portion:
 has an opening at an end thereof, 
 is bottomed and tubular, 
 has, on an inner surface at a position near an insertion opening through which the measurement probe is inserted, a light absorption portion provided with a light absorption member that absorbs light, and 
 has the reference reflection plate provided on a bottom portion thereof. 
 
     
     
       8. The calibration apparatus according to  claim 7 , wherein the insertion portion is bent. 
     
     
       9. The calibration apparatus according to  claim 1 , further comprising:
 a first container provided inside thereof with an optical absorption member that absorbs light; 
 a second container that accommodates the reference reflection plate; 
 a change portion that changes, with respect to the insertion portion, positions of the first container and the second container; and 
 a change drive unit that drives the change unit. 
 
     
     
       10. A calibration method of obtaining calibration data using a calibration apparatus with respect to an optical measurement apparatus that includes: a measurement probe having an illumination fiber that irradiates to an object to be measured illumination light including at least light of wavelength to be measured and a plurality of detection fibers that receive, at different angles, returned light of the illumination light reflected and/or scattered by the object to be measured; and a plurality of detection units that detect the returned light respectively received by the plurality of detection fibers, the calibration method comprising:
 a first step of obtaining data for internal reflection calibration of the measurement probe detected by the detection units when the measurement probe is caused to irradiate the illumination light to an insertion portion that is provided, inside the calibration apparatus, with a light absorption member that absorbs light; and 
 a second step of obtaining reference reflection plate calibration data detected by the detection units when the measurement probe irradiates the illumination light to a reference reflection plate in the calibration apparatus, the reference reflection plate being arranged at a position away from a distal end of the measurement probe by a predetermined distance and having uniform reflectivity of light over a range of the wavelength to be measured in an irradiation plane of the illumination light, 
 wherein a material forming the reference reflection plate has a scattering mean free path that is greater than a spatial coherence length at the predetermined distance.